Keyframe toggle visibilty for child object using parent object in outliner?
Consider a [driver] which assigns to the child render state the value of the parent render state.  If you have never done this before it really is the best.

All the navigation described below might best be understood with a video at some famous video site ... Search Blender Driver Tutorial... but I will provide a modest navigation here.

Use the other mouse click to bring up the menu on the EYE of the child to add driver.  When finished the purple circle will appear as depicted below.

Switch to the graph window as indicated above and view the [drivers] via the button next to the word Key on the menu.  Click on the Restrict Render on the left side to see the driver settings.  

Make these settings.  Just as in the image above.

Type: Averaged Value.  

Prop: name of your parent.

Path: hide_render (which was copied as a data path)

Thus you  need to key frame the Restrict Render Eye of the parent only.


There are ways to copy and paste drivers from the menu of the Eye of the child.  You need to do this for each of the remaining 20 or so child objects.



In your case you have parented the children to the parent. The driver mechanism can allows you to choose any object to be the source of the render state.